Valve actuation in an internal combustion engine is required in order for the engine to produce positive power, as well as for engine braking. During positive power, intake valves may be opened to admit fuel and air into a cylinder for combustion. The exhaust valves may be opened to allow combustion gas to escape from the cylinder.
Internal combustion engines may not only be used to produce positive power, but to also provide bleeder type engine braking. During bleeder engine braking, in addition to the main exhaust valve event, one or more exhaust valve(s) may be held slightly open by an amount sufficient to provide bleeder braking throughout the remaining engine cycles (i.e., the intake, compression, and expansion cycles for a full-cycle bleeder brake) The initial opening of the exhaust valves in a bleeder braking operation may be in advance of top dead center (TDC) of the compression stroke, and is preferably near a bottom dead center (BDC) point between the intake and compression cycles. As such, a bleeder type engine brake may require much lower force to actuate the valves, and generate less noise due to continuous bleeding instead of the rapid blow-down of a compression-release type brake. Thus, an engine bleeder brake can have significant advantages.
During start-up and shut-down, an internal combustion engine may shudder and shake as it compresses air at low engine speeds. Moreover, it may be particularly difficult to achieve adequately high cranking speeds, to charge and activate the valve actuation system with hydraulic fluid when the fluid is cold and has a higher viscosity. Holding open an intake and/or exhaust valve during engine start-up may decompress the cylinder so that the piston may move towards a TDC position more easily. An engine decompression system may hold open one or more intake and/or exhaust valves in an engine cylinder during the start-up or shut-down of the engine. Thus, just when the engine is about to shut down, the engine decompression system may be activated to hold the intake and/or exhaust valve(s) open by a lift sufficient to decompress the engine. The valve lift may be controlled so that the piston may not run into the valve, but the lift may be adequate to let the pressure in and out of the cylinder.
An engine decompression system of the type described herein may be particularly useful in cold weather conditions, when cranking battery power is lower, cranking time to start-up is increased, the fuel/air mixture is less likely to ignite, and the engine is more difficult to turn over. In addition, engine decompression, which may reduce battery power and starter system requirements, may result in lower weight components, which permit increased fuel efficiency, and avoidance or reduction in the need for additional starting aids. Reduction in start-up time resulting from use of a decompression system may also provide emissions benefits. Decompression shutdown may also result in a randomization of engine stopping angle, which may aid in a more evenly distributed wearing of the starter gear and the flywheel ring gear. Accordingly, advantages such as these, but not limited to the foregoing, may be realized by use of one or more of the embodiments of the invention described herein.
Various embodiments of the present invention may meet one or more of the aforementioned needs and provide other benefits as well.